The present disclosure relates to IC tags for performing non-contact communication with a reader/writer and to electronic apparatuses mounted with the IC tag.
IC tags, which perform non-contact communication with an adjacent reader/writer to carry out authentication processing or the like, are widely prevailing. Particularly, so-called passive IC tags, which have no power source such as battery cell in the IC tag itself but operate using the power obtained by receiving radio waves from a reader/writer and accumulated in a capacitor or the like, are prevailing due to its usability.
An IC tag is configured including component parts such as IC chip performing communication processing, mounted on a circuit substrate formed with an antenna pattern for receiving a radio wave from a reader/writer. In order to efficiently receive a radio wave from the reader/writer, the antenna pattern is disposed in a relatively large area in a coil shape on the circuit substrate. Generally, in a central area enclosed by the coil-shaped antenna pattern, component parts such as an IC chip, a capacitor and the like are disposed. When carrying out authentication processing using an IC tag, for example, a piece of information stored in a memory of the IC chip is transmitted to a reader/writer, and a piece of information transmitted from the reader/writer is written on the memory of the IC chip; thus communication processing is carried out by the IC tag itself.
Thus, radio communication with a reader/writer is possible by an IC tag itself. For example, electronic money cards, ticket cards, authentication cards and the like, in which a circuit substrate including an IC tag is packaged in a card or the like, are prevailing.
On the other hand, various kinds of electronic apparatuses such as mobile phone terminal in which an IC tag is embedded are also prevailing. In IC tags embedded in the electronic apparatus, basic configuration of the IC tag itself is the same. Some electronic apparatuses embedded with an IC tag perform a certain operation responding to a communication status of the IC tag. For example, it is detected that an IC tag starts communication with a reader/writer, and the power for the electronic apparatus main body is then turned on using the initiation of communication as a trigger.
FIG. 10 is an illustration showing an example of configuration of an IC tag embedded in a conventional electronic apparatus; and FIG. 11 is a cross-sectional view taken along a line A-A in FIG. 10.
A coil antenna 2 including a conducting layer strip, which is laid around in a coil-like shape, is disposed in an outer area of a surface of a rectangular substrate 1 made of resin material. In the example shown in FIG. 10, the coil antenna 2 has a configuration in which the conducting layer is laid around by three turns.
An end 2a of the coil antenna 2 at an outer periphery side is connected to a wiring pattern 2g at a rear surface side of the substrate 1 via a through hole 3b. The wiring pattern 2g at the rear surface side is further connected to a wiring pattern 2d of the coil antenna 2 provided in an inner area of the surface via other through hole 3b. An end 2b of the coil antenna 2 at an inner side is connected to a wiring pattern 2c. 
Thus, the wiring pattern 2c and the wiring pattern 2d, which are connected to one end and other end of the coil antenna 2, are connected to an IC chip 4 mounted on the surface of the substrate 1. The IC chip 4 is a chip including a circuit which performs processing of radio communication with a reader/writer. Thus, by connecting the IC chip 4 to the coil antenna 2, non-contact communication with a reader/writer is made possible.
In the example of IC tag shown in FIG. 10, wiring patterns 2e and 2f each branched at a point in a halfway of wiring patterns 2c and 2d connected to the IC chip 4 on the surface of the substrate 1, and the wiring patterns 2e and 2f are connect to pads 5a and 5b on the surface of the substrate 1. The pads 5a and 5b are electrode parts each of which functions as a connection terminal to an external circuit.
The IC tag including the pads 5a and 5b as described above is connected to an external circuit in an electronic apparatus as shown in FIG. 12. That is, the pads 5a and 5b provided to the IC tag are connected to the input terminals 7a and 7b of a rectifier circuit 7 via extension wires 6a and 6b. In the rectifier circuit 7, the input terminals 7a and 7b are connected to a rectifying diode bridge 7c and signals obtained at the input terminals 7a and 7b are transmitted to the rectifying diode bridge 7c via capacitors C1 and C2 and rectified signal is outputted. A capacitor C3 is connected to the rectifying diode bridge 7c at an output side thereof. The signal rectified by the rectifier circuit 7 is supplied to a detection circuit 8.
Receiving an input signal exceeding a predetermined threshold value from the IC tag via the rectifier circuit 7, the detection circuit 8 outputs a detection signal. That is, when the IC tag is positioned close to a reader/writer and receives a signal transmitted from the reader/writer with the coil antenna 2, the detection circuit 8 detects the level of the received signal. By using the detection signal obtained from the detection circuit 8 as a trigger, the electronic apparatus can perform various processing such as start-up of the electronic apparatus itself at a moment of, for example, approximation to the reader/writer.
The capacitors C1 and C2 are for galvanically-isolating the circuit on the IC tag from an external circuit to avoid any influence on the circuit on the IC tag and the external circuit. That is, the coil antenna 2 and the IC chip 4 in the IC tag are configured so as to perform non-contact communication with a reader/writer at a prescribed resonant frequency. Here, if the external circuit is directly connected to the IC tag without being interposed by a capacitor, electrical characteristics such as resonant frequency may be disturbed resulting in a reduction of performance as the IC tag. Therefore, in order to avoid such inconvenient influence, the capacitors C1 and C2 are connected.
Japanese Unexamined Patent Application Publication No. 2007-6029 teaches a configuration of a mobile phone terminal including an IC tag as an example of electronic apparatus which includes an IC tag.